Spell check is not the only problem. If you hear it wrong, it gets written wrong. You see it written wrong and it becomes right in your head. The cycle repeats until the incorrect becomes acceptable and our language perishes.

Don't even ask me about "for all intensive purposes."

Irrespective

irregardless.

Have mercy. It shows up in the dictionary.

Smith and Western.
I heard Shakespeare made up a lot of the words we use today, but language can be taken a long way from the classic format once it becomes slang.
spellcheck is great for checking. Never without a backup. It's easy to forget how hard it was to learn to spell because it was so long ago but spellcheck won't teach much. If only the English language made more sense. Maybe sometimes reading like it sounds would help. It's also 'funny' how a wrong letter can mean something completely different.